177Lu‐labeled monomeric,dimeric and multimeric RGD peptides for the therapy of tumors expressing α(ν)β(3) integrins

The conjugation of peptides to gold nanoparticles (AuNPs) produces biocompatible and stable multimeric systems with target‐specific molecular recognition. Peptides based on the cyclic Arg‐Gly‐Asp (RGD) sequence have been reported as high‐affinity agents for the α(ν)β(3) integrin. The aim of this research was to prepare a multimeric system of ¹⁷⁷Lu‐labeled gold nanoparticles conjugated to c(RGDfK)C (cyclo(Arg‐Gly‐Asp‐Phe‐Lys)Cys) and to compare the radiation‐absorbed dose with that of ¹⁷⁷Lu‐labeled monomeric and dimeric RGD peptides to α(ν)β(3) integrin‐positive U87MG tumors in mice. DOTA‐GGC (1,4,7,10‐tetraazacyclododecane‐N‐N′,N″,N?‐tetraacetic acid‐Gly‐Gly‐Cys) and c(RGDfK)C peptides were synthesized and conjugated to AuNPs by a spontaneous reaction of the thiol groups. Transmission electron microscopy, ultraviolet–visible, X‐ray photoelectron spectroscopy, Raman and far‐infrared spectroscopy techniques demonstrated that AuNPs were functionalized with the peptides. For the ¹⁷⁷Lu‐AuNP‐c(RGDfK)C to be obtained, the ¹⁷⁷Lu‐DOTA‐GGC radiopeptide was first prepared and added to a solution of AuNPs followed by c(RGDfK)C (25 µl, 5 µ m ) at 18 °C for 15 min. ¹⁷⁷Lu‐DOTA‐GGC, ¹⁷⁷Lu‐DOTA‐cRGDfK and ¹⁷⁷Lu‐DOTA‐E‐c(RGDfK)₂ were prepared by adding ¹⁷⁷LuCl₃ (370 MBq) to 5 µl (1 mg/ml) of the DOTA derivative diluted with 50 µl of 1 m acetate buffer pH 5. The mixture was incubated at 90 °C in a block heater for 30 min. Radiochemical purity was determined by ultrafiltration and HPLC analyses. Biokinetic studies were accomplished in athymic mice with U87MG‐induced tumors. The radiochemical purity for all ¹⁷⁷Lu‐RGD derivatives was 96 ± 2%. ¹⁷⁷Lu‐absorbed doses per injected activity delivered to U87MG tumors were 0.357 ± 0.052 Gy/MBq (multimer), 0.252 ± 0.027 Gy/MBq (dimer) and 0.102 ± 0.018 Gy/MBq (monomer). ¹⁷⁷Lu‐labeled dimeric and multimeric RGD peptides demonstrated properties suitable for targeted radionuclide therapy of tumors expressing α(ν)β(3) integrins. Copyright © 2012 John Wiley & Sons, Ltd.     

The in vivo disposition and in vitro transmembrane transport of two model radiometabolites of DOTA‐conjugated receptor‐specific peptides labelled with 177Lu

In vivo metabolism of the radiolabelled receptor‐specific peptides has been described; however, information regarding the pharmacokinetic behaviour of the degradation products within the body is very scarce. The present study was designed to obtain new knowledge on the disposition and elimination of low‐molecular radiometabolites of receptor‐specific peptides in the organism and to reveal the potential involvement of selected membrane transport mechanisms in the cellular uptake of radiometabolites, especially in the kidney. The study compared pharmacokinetics of two radiometabolites: a final metabolite of somatostatin analogues, ¹⁷⁷Lu‐DOTA‐DPhe, and a tripeptide metabolite of ¹⁷⁷Lu‐DOTA‐minigastrin 11, ¹⁷⁷Lu‐DOTA‐DGlu‐Ala‐Tyr. Their pharmacokinetics was compared with that of respective parent ¹⁷⁷Lu‐radiopeptide. Both radiometabolites exhibited relative rapid clearing from most body tissues in rats in vivo along with predominant renal excretion. The long‐term renal retention of the smaller radiometabolite ¹⁷⁷Lu‐DOTA‐DPhe was lower than that of ¹⁷⁷Lu‐DOTA‐DGlu‐Ala‐Tyr. An uptake of ¹⁷⁷Lu‐DOTA‐DPhe by human renal influx transporter organic cation transporter 2 was found in vitro in a cellular model. The study brings the first experimental data on the in vivo pharmacokinetics of radiometabolites of receptor‐specific somatostatin and gastrin analogues. The found results may indicate a negative correlation between the degree of decomposition of the parent peptide chain and the renal retention of the metabolite.     

Preparation of 177Lu‐labeled Nimotuzumab for radioimmunotherapy of EGFR‐positive cancers: Comparison of DOTA and CHX‐A″‐DTPA as bifunctional chelators

This study was aimed at evaluating the role of bifunctional chelators DOTA‐NCS and CHX‐A″‐DTPA‐NCS used for conjugating ¹⁷⁷Lu with Nimotuzumab on the radiochemical yields, purity, in vitro stability, and specificity of the radioimmunoconjugates to EGFR. Two immunoconjugates were prepared wherein Nimotuzumab was conjugated with the acyclic ligand p‐NCS‐Bn‐CHX‐A″‐DTPA and macrocyclic ligand p‐NCS‐Bn‐DOTA. These were radiolabeled with ¹⁷⁷Lu, purified on PD‐10 column, and characterized by SE‐HPLC. In vitro stability was determined up to 4 days post preparation. Specificity of the radioimmunoconjugates was ascertained by in vitro studies in A431 cells while the biodistribution patterns were studied in normal Swiss mice up to 96 hours post injection. Four to five molecules of CHX‐A″‐DTPA/DOTA were attached to one molecule of Nimotuzumab. Radiochemical purity of both ¹⁷⁷Lu‐CHX‐A″‐DTPA‐Nimotuzumab and ¹⁷⁷Lu‐DOTA‐Nimotuzumab was determined to be greater than 98%. Both the radioimmunoconjugates exhibited good in vitro stability at 37°C up to 4 days post preparation in saline, and their clearance was largely by the hepatobiliary route. The DOTA‐ and CHX‐A″‐DTPA‐based radioimmunoconjugates could be prepared with good radiochemical purity, in vitro stability, and specificity to EGFR. Further studies in EGFR‐positive cancers would pave way for them for use in the clinics.     

99mTc‐(EDDA/tricine)‐HYNIC‐GnRH analogue as a potential imaging probe for diagnosis of prostate cancer

Prostate cancer is a serious threat to men's health, so it is necessary to develop the techniques for early detection of this malignancy. Radiolabeled peptides are the useful tools for diagnosis of prostate cancer. In this research, we designed a new HYNIC‐conjugated GnRH analogue and labeled it by ^99mTc with tricine/EDDA as coligands. We used aminohexanoic acid (Ahx) as a hydrocarbon linker to generate ^99mTc‐(tricine/EDDA)‐HYNIC‐Ahx‐[DLys⁶]GnRH. The radiopeptide exhibited high radiochemical purity and stability in solution and serum. Two human prostate cancer cell lines LN‐CaP and DU‐145 were used for cellular experiments. The binding specificity and affinity of radiopeptide for LN‐CaP were superior to DU‐145 cells. The K_d values for LN‐CaP and DU‐145 cells were 41.91 ± 7.03 nM and 55.96 ± 10.56 nM, respectively. High kidney uptake proved that the main excretion route of radiopeptide was through the urinary system. The tumor/muscle ratio of ^99mTc‐HYNIC‐Ahx‐[DLys⁶]GnRH was 4.14 at 1 hr p.i. that decreased to 2.41 at 4 hr p.i. in LN‐CaP tumor‐xenografted nude mice. The blocking experiment revealed that the tumor uptake was receptor‐mediated. The lesion was visualized clearly using ^99mTc‐[DLys⁶]GnRH at 1 hr p.i. Accordingly, this research highlights the capability of ^99mTc‐(tricine/EDDA)‐HYNIC‐Ahx‐[DLys⁶]GnRH peptide as a promising agent for GnRHR‐expressing tumor imaging.     

Preclinical evaluation of potential infection‐imaging probe [68Ga]Ga‐DOTA‐K‐A9 in sterile and infectious inflammation

The development of bacteria‐specific infection radiotracers is of considerable interest to improve diagnostic accuracy and enabling therapy monitoring. The aim of this study was to determine if the previously reported radiolabelled 1,4,7,10‐tetraazacyclododecane‐N,N′,N″,N?‐tetraacetic acid (DOTA) conjugated peptide [⁶⁸Ga]Ga‐DOTA‐K‐A9 could detect a staphylococcal infection in vivo and distinguish it from aseptic inflammation. An optimized [⁶⁸Ga]Ga‐DOTA‐K‐A9 synthesis omitting the use of acetone was developed, yielding 93 ± 0.9% radiochemical purity. The in vivo infection binding specificity of [⁶⁸Ga]Ga‐DOTA‐K‐A9 was evaluated by micro positron emission tomography/magnetic resonance imaging of 15 mice with either subcutaneous Staphylococcus aureus infection or turpentine‐induced inflammation and compared with 2‐deoxy‐2‐[¹⁸F]fluoro‐D‐glucose ([¹⁸F]FDG). The scans showed that [⁶⁸Ga]Ga‐DOTA‐K‐A9 accumulated in all the infected mice at injected doses ≥3.6 MBq. However, the tracer was not found to be selective towards infection, since the [⁶⁸Ga]Ga‐DOTA‐K‐A9 also accumulated in mice with inflammation. In a concurrent in vitro binding evaluation performed with a 5‐carboxytetramethylrhodamine (TAMRA) fluorescence analogue of the peptide, TAMRA‐K‐A9, the microscopy results suggested that TAMRA‐K‐A9 bound to an intracellular epitope and therefore preferentially targeted dead bacteria. Thus, the [⁶⁸Ga]Ga‐DOTA‐K‐A9 uptake observed in vivo is presumably a combination of local hyperemia, vascular leakiness and/or binding to an epitope present in dead bacteria.     

Single vial kit formulation of DOTATATE for preparation of 177Lu‐labeled therapeutic radiopharmaceutical at hospital radiopharmacy

The clinical applications of radiolabeled somatostatin analogue ¹⁷⁷Lu‐DOTA‐Tyr³‐Thr⁸‐Octreotide (¹⁷⁷Lu‐DOTATATE) constitute a promising treatment option for patients with disseminated and inoperable neuroendocrine (NET) tumors. Formulation of ¹⁷⁷Lu‐DOTATATE in hospital radiopharmacy under aseptic conditions in a safe and reliable manner is a major constraint for its extensive use. The present work was intended to develop a kit for the safe preparation of the therapeutic radiopharmaceutical, viz. ¹⁷⁷Lu‐DOTATATE of high quality that can be easily adapted at conventional hospital radiopharmacies. Single vial kits of DOTATATE were formulated and evaluated for suitability for radiolabeling as well as stability on its storage. Patient dose of ¹⁷⁷Lu‐DOTATATE (7.4 GBq) could be successfully prepared using semi‐automated in‐house setup that assures safe handling and high yields of product of pharmaceutical purity suitable for clinical use. Fast clearance of activity via renal route was observed in preclinical biodistribution studies of ¹⁷⁷Lu‐DOTATATE carried out in normal Swiss mice. Deployment of in‐house produced ¹⁷⁷LuCl₃, cold kits and easy adaptability of synthesis setup at hospital radiopharmacy for preparation is likely to expand applications of peptide receptor radionuclide therapy.     

Radiolabeling,quality control,biodistribution, and imaging studies of 177Lu‐ibandronate

The purposes of this study were as follows: (1) to radiolabel ibandronic acid (IBA, a third‐generation bisphosphonate) with ¹⁷⁷Lu, investigating optimal labeling conditions, and (2) to analyze biodistribution and imaging properties of intravenous ¹⁷⁷Lu‐ibandronate (¹⁷⁷Lu‐IBA) administered in animals. ¹⁷⁷Lu‐labeled methylene diphosphonate (¹⁷⁷Lu‐MDP) served as a comparator agent. Differing proportions of IBA solution and ¹⁷⁷LuCl₃ solution were combined to determine an optimal ratio for radiolabeling purposes, varying pH, temperature, and time to establish ideal reactivity conditions. Radiochemical purity of the labeled compounds was then assessed by paper chromatography. In vitro and in vivo stabilities were also measured at specific time intervals. In Kunming mice, biodistributions of ¹⁷⁷Lu‐IBA and ¹⁷⁷Lu‐MDP and respective agent activities in various organs were monitored by gamma counter, and we performed single photon computed tomography/computed tomography (SPECT/CT) imaging of ¹⁷⁷Lu‐IBA in normal New Zealand White rabbits. Radiolabeling yields for ¹⁷⁷Lu‐IBA proved to be >97% within 30 minutes at 90°C, and its radiochemical purity ensured stability in vitro and in vivo. Furthermore, we found that ¹⁷⁷Lu‐IBA is readily soluble in water, showing higher skeletal uptake than ¹⁷⁷Lu‐MDP but lower uptake by liver and spleen. The image quality of ¹⁷⁷Lu‐IBA was so clear that even after 6 days, analysis was still feasible.     

Exploring the radiosynthesis and in vitro characteristics of [68Ga]Ga‐DOTA‐Siglec‐9

Vascular adhesion protein 1 is a leukocyte homing‐associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283–297 of sialic acid‐binding IgG‐like lectin 9 (Siglec‐9) “CARLSLSWRGLTLCPSK” bind to vascular adhesion protein 1 and hence makes the radioactive analogues of this compound ([⁶⁸Ga]Ga‐DOTA‐Siglec‐9) interesting as a noninvasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 are presented and compared with previously published methods. A simple, robust radiosynthesis of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 with a yield of 62% (non decay‐corrected) was identified, and it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 were analyzed in vitro in mouse, rat, rabbit, pig, and human plasma and compared with in vivo pig results. The plasma in vitro protein binding of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 was the lowest in the pig followed by rabbit, human, rat, and mouse. It was considerably higher in the in vivo pig experiments. The in vivo stability in pigs was lower than the in vitro stability. Despite considerable species differences, the observed characteristics of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 are suitable as a positron emission tomography tracer.     

A “mix‐and‐use” approach for formulation of human clinical doses of 177Lu‐DOTMP at hospital radiopharmacy for management of pain arising from skeletal metastases

Use of bone‐seeking radiopharmaceuticals is an established modality in the palliative care of pain due to skeletal metastases. ¹⁷⁷Lu‐DOTMP is a promising radiopharmaceutical for this application owing to the ideally suited decay properties of ¹⁷⁷Lu and excellent thermodynamic stability and kinetic rigidity of the macrocyclic complex. The aim of the present study is to develop a robust and easily adaptable protocol for formulation of clinical doses of ¹⁷⁷Lu‐DOTMP at hospital radiopharmacy. After extensive radiochemical studies, an optimized strategy for formulation of clinical doses of ¹⁷⁷Lu‐DOTMP was developed, which involves simple mixing of approximately 3.7 GBq of ¹⁷⁷Lu activity as ¹⁷⁷LuCl₃ solution to an aqueous solution containing 5 mg of DOTMP and 8 mg of NaHCO₃. The proposed protocol yielded ¹⁷⁷Lu‐DOTMP with >98% radiochemical purity, and the resultant formulation showed excellent in vitro stability and desired pharmacokinetic properties in animal model. Preliminary clinical investigations in 5 patients showed specific skeletal accumulation with preferential localization in the osteoblastic lesion sites and almost no uptake in soft tissue or any other major nontarget organ. The developed “mix‐and‐use” strategy would be useful for large number of nuclear medicine centers having access to ¹⁷⁷Lu activity and would thereby accelerate the clinical translation of ¹⁷⁷Lu‐DOTMP.     

Synthesis and biological evaluation of 68Ga‐labeled Pteroyl‐Lys conjugates for folate receptor‐targeted tumor imaging

In order to develop novel ⁶⁸Ga‐labeled PET tracers for folate receptor imaging, two DOTA‐conjugated Pteroyl‐Lys derivatives, Pteroyl‐Lys‐DOTA and Pteroyl‐Lys‐DAV‐DOTA, were designed, synthesized and radiolabeled with ⁶⁸Ga. Biological evaluations of the two radiotracers were performed with FR‐positive KB cell line and athymic nude mice bearing KB tumors. Both ⁶⁸Ga‐DOTA‐Lys‐Pteroyl and ⁶⁸Ga‐DOTA‐DAV‐Lys‐Pteroyl exhibited receptor specific binding in KB cells in vitro. The tumor uptake values of ⁶⁸Ga‐DOTA‐Lys‐Pteroyl and ⁶⁸Ga‐DOTA‐DAV‐Lys‐Pteroy were 10.06 ± 0.59%ID/g and 11.05 ± 0.60%ID/g at 2 h post‐injection, respectively. Flank KB tumor was clearly visualized with ⁶⁸Ga‐DOTA‐DAV‐Lys‐Pteroyl by Micro‐PET imaging at 2 h post‐injection, suggesting the feasibility of using ⁶⁸Ga‐labeled Pteroyl‐Lys conjugates as a novel class of FR targeted probes.     

Development of a novel,fibrin‐specific PET tracer

Fibrin deposition is observed in several diseases such as atherosclerosis, deep vein thrombosis, and also tumors, where it contributes to the formation of mature tumor stroma. The aim of this study was to develop a gallium‐labeled peptide tracer on the basis of the fibrin‐targeting peptide Epep for PET imaging of fibrin deposition. For this purpose, the peptide Epep was modified with a NOTA moiety for radiolabeling with ⁶⁷Ga and ⁶⁸Ga and compared with the earlier validated ¹¹¹In‐DOTA‐Epep tracer. In vitro binding assays of ⁶⁷Ga‐NOTA‐Epep displayed an enhanced retention as compared to previously published data showing binding of ¹¹¹In‐DOTA‐Epep to human (84.0 ± 0.6 vs 66.6 ± 1.4 %Dose) and mouse derived fibrin clots (83.5 ± 1.7 vs 74.2 ± 2.4% Dose). In vivo blood kinetics displayed a bi‐phasic elimination profile (t_1/2,_α = 2.6 ± 1.0 minutes and t_1/2,_β = 15.8 ± 1.3 minutes) and ex vivo biodistribution showed low blood values at 4 hours post injection and a low uptake in nontarget tissue (<0.2 %ID/g; kidneys, 1.9%ID/g). In conclusion, taking into account the ease of radiolabeling and the promising in vitro and in vivo studies, gallium‐labeled Epep displays the potential for further development towards a PET tracer for fibrin deposition.     

Preparation of clinical‐scale 177Lu‐Rituximab: Optimization of protocols for conjugation,radiolabeling, and freeze‐dried kit formulation

Rituximab is a monoclonal chimeric antibody, which has been approved by the US Food and Drug Administration for immunotherapy of non–Hodgkin lymphoma. Bexxar and Zevalin are the two other approved radiolabeled antibodies for radioimmunotherapy of non–Hodgkin lymphoma; however, they are of murine origin that reduces their treatment efficacy. So as to circumvent this, efforts have been made to radiolabel Rituximab with various therapeutic radioisotopes. In the present study, an effort has been made to optimize the conjugation (bifunctional chelating agent and antibody) and radiolabeling procedures for the preparation of clinical‐scale ¹⁷⁷Lu‐labeled Rituximab. An attempt was also made to prepare the freeze‐dried Rituximab kit for the easy and convenient clinical translation of the agent. Clinical‐scale ¹⁷⁷Lu‐Rituximab (40 mCi, 1.48 GBq) was prepared with >95% radiochemical purity using the kit. Biological evaluation of ¹⁷⁷Lu‐Rituximab was performed by in vitro cell binding studies in Raji cell lines, which showed satisfactory binding at 4°C and 37°C. Pharmacokinetic behavior of the agent, evaluated by biodistribution studies in normal Swiss mice, revealed high blood and liver uptake at the initial time points, although it exhibited slow and gradual clearance with time. The study indicates that clinical‐scale ¹⁷⁷Lu‐Rituximab could be conveniently formulated using the methodology described in the present article.     

Cerenkov luminescence imaging of αvβ6 integrin expressing tumors using 90Y‐labeled peptides

Cerenkov luminescence imaging (CLI) is an emerging preclinical molecular imaging modality that tracks the radiation emitted in the visible spectrum by fast moving charged decay products of radionuclides. The aim of this study was in vitro and in vivo evaluation of the two radiotracers, ⁹⁰Y‐DOTA‐PEG₂₈‐A20FMDV2 (⁹⁰Y‐1) and ⁹⁰Y‐DOTA‐Ahx‐A20FMDV2 (⁹⁰Y‐2) (>99% radiochemical purity, 3.7 GBq/µmol specific activity) for noninvasive assessment of tumors expressing the integrin α_vβ₆ and their future use in tumor targeted radiotherapy. Cell binding and internalization in α_vβ₆‐positive cells was ⁹⁰Y‐1: 10.1 ± 0.8%, 50.3 ± 2.1%; ⁹⁰Y‐2: 22.4 ± 1.7%, 44.7 ± 1.5% with <5% binding to α_vβ₆‐negative control cells. Biodistribution studies showed maximum α_vβ₆‐positive tumor uptake of the radiotracers at 1‐h post injection (p.i.) (⁹⁰Y‐1: 0.64 ± 0.15% ID/g; ⁹⁰Y‐2: 0.34 ± 0.11% ID/g) with high renal uptake (>25% ID/g at 24 h). Because of the lower tumor uptake and high radioactivity accumulation in kidneys (that could not be reduced by pre‐administration of either lysine or furosemide), the luminescence signal from the α_vβ₆‐positive tumor was not clearly detectable in CLI images. The studies suggest that CLI is useful for indicating major organ uptake for both radiotracers; however, it reaches its limitation when there is low signal‐to‐noise ratio.     

Multifunctional targeted therapy system based on 99mTc/177Lu‐labeled gold nanoparticles‐Tat(49–57)‐Lys3‐bombesin internalized in nuclei of prostate cancer cells

Radiolabeled gold nanoparticles may function simultaneously as radiotherapy and thermal ablation systems. The gastrin‐releasing peptide receptor (GRP‐r) is overexpressed in prostate cancer, and Lys³‐bombesin is a peptide that binds with high affinity to the GRP‐r. HIV Tat(49–57) is a cell‐penetrating peptide that reaches the DNA. In cancer cells, ¹⁷⁷Lu shows efficient crossfire effect, whereas ^99mTc that is internalized in the cancer cell nuclei acts as an effective system of targeted radiotherapy because of the biological Auger effect. The aim of this research was to evaluate the in vitro potential of ^99mTc‐labeled and ¹⁷⁷Lu‐labeled gold nanoparticles conjugated to Tat(49–57)‐Lys³‐bombesin peptides (^99mTc/¹⁷⁷Lu‐AuNP‐Tat‐BN) as a plasmonic photothermal therapy and targeted radiotherapy system in PC3 prostate cancer cells. Peptides were conjugated to AuNPs (5 nm) by spontaneous reaction with the thiol group of cysteine (Cys). The effect on PC3 cell viability after laser heating of the AuNP‐Tat‐BN incubated with the cancer cells was conducted using an Nd:YAG laser pulsed for 5 ns at 532 nm (0.65 W/cm²). For the ^99mTc/¹⁷⁷Lu‐AuNP‐Tat‐BN to be obtained, the ¹⁷⁷Lu‐DOTA‐Gly‐Gly‐Cys and ^99mTc‐HYNIC‐octreotide radiopeptides were first prepared and added simultaneously to a solution of AuNP‐Tat‐BN. ^99mTc/¹⁷⁷Lu‐AuNP‐Tat‐BN (20 Bq/cell) was incubated with PC3 cells, and the effect on the cell proliferation was evaluated after 3 days. Fluorescence images of ^99mTc/¹⁷⁷Lu‐AuNP‐Tat‐BN internalized in nuclei of PC3 were also obtained. After laser irradiation, the presence of AuNP‐Tat‐BN caused a significant increase in the temperature of the medium (46.4 vs 39.5 °C of that without AuNP) resulting in a significant decrease in PC3 cell viability down to 1.3%. After treatment with ^99mTc/¹⁷⁷Lu‐AuNP‐Tat‐BN, the PC3 cell proliferation was inhibited. The nanosystem exhibited properties suitable for plasmonic photothermal therapy and targeted radiotherapy in the treatment of prostate cancer.     

Design and development of the theranostic pair 177Lu‐OPS201/68Ga‐OPS202 for targeting somatostatin receptor expressing tumors

Radiolabeled somatostatin receptor (sstr) antagonists have shown superiority in different preclinical and clinical settings compared with the well‐established and clinically used agonists for targeting sstr‐expressing tumors, with regard to pharmacokinetics, tumor uptake, and retention. The theranostic pair ¹⁷⁷Lu‐OPS201/⁶⁸Ga‐OPS202, based on the sstr2 antagonist JR11 (Cpa‐c[d ‐Cys‐Aph(Hor)‐d ‐Aph(Cbm)‐Lys‐Thr‐Cys]‐d ‐Tyr‐NH₂), is the most advanced pair of the antagonist family in terms of preclinical development and is currently under clinical evaluation. OPS201 and OPS202 share the same amino acid sequence (JR11) but feature different conjugated chelators needed for radiolabeling, DOTA for OPS201 and NODAGA for OPS202. In this review, the design and development of the peptidic analog, JR11, and the selection of chelators and radiometals that led to ¹⁷⁷Lu‐OPS201/⁶⁸Ga‐OPS202 are discussed. Furthermore, the preclinical evaluation of both radiolabeled analogs from bench to bedside and the clinical trials involving the theranostic pair are presented.     

Prospects of medium specific activity 177Lu in targeted therapy of prostate cancer using 177Lu‐labeled PSMA inhibitor

Targeted radionuclide therapy using ¹⁷⁷Lu‐labeled peptidomimetic inhibitor of prostate specific membrane antigen (PSMA) viz. PSMA‐617 is emerging as one the most effective strategies for management of metastatic prostate cancer, which is one of the leading causes of cancer related death. The aim of the present study is to develop a robust and easily adaptable protocol for formulation of therapeutic dose of ¹⁷⁷Lu‐PSMA‐617 at hospital radiopharmacy using moderate specific activity ¹⁷⁷Lu available at an affordable cost. Extensive radiochemical studies were performed to optimize the required [PSMA‐617] / [Lu] ratio and other parameters to formulate 7.4 GBq dose of ¹⁷⁷Lu‐PSMA‐617. Based on these, 7.4 GBq therapeutic dose of ¹⁷⁷Lu‐PSMA‐617 was formulated by incubating 160 µg of PSMA‐617 with indigenously produced ¹⁷⁷LuCl₃ (555 GBq/µg specific activity of ¹⁷⁷Lu) at 90 °C for 30 min. The radiochemical purity of the formulation was 98.3 ± 0.6% (n = 7) which was retained to the extent of >95% after 7 d in normal saline at room temperature and >96% after 2 d in human serum at 37 °C. Preliminary clinical studies showed specific targeting of the agent in the lesion sites and similar physiological distribution as in diagnostic ⁶⁸Ga‐PSMA‐11 PET scans performed earlier. The developed optimized protocol for formulating therapeutic dose of ¹⁷⁷Lu‐PSMA‐617 could be useful for large number of nuclear medicine therapy clinics across the world having access to moderate specific activity ¹⁷⁷Lu at an affordable cost.     

Synthesis and in vivo evaluation in mice of [123I]‐(4‐fluorophenyl)[1‐(3‐iodophenethyl)piperidin‐4‐yl]methanone as a potential SPECT‐tracer for the serotonin 5‐HT2A receptor

This work reports the synthesis, radiolabelling and in vivo evaluation in NMRI mice of [¹²³I]‐(4‐fluorophenyl)[1‐(3‐iodophenethyl)piperidin‐4‐yl]methanone ([¹²³I]‐3‐I‐CO) as a potential SPECT tracer for the 5‐HT_2A receptor. The tributylstannylprecursor was synthesized with a 15% overall yield. Radiolabelling was performed using an electrophilic iododestannylation with yields of 85%. Radiochemical purity was always >95%. Log P was determined to be 3.10±0.10. The tracer showed good uptake in mouse brain (6.3±1.3% ID/g tissue at 10 min p.i., 2±0.36% ID/g tissue at 1 h p.i.). These results warrant further research in larger animals to determine suitability of [¹²³I]‐3‐I‐CO as a 5‐HT_2A tracer. Copyright © 2007 John Wiley & Sons, Ltd.     

Binding of endomorphin‐2 to μ‐opioid receptors in experimental mouse mammary adenocarcinoma

Abstract: Endomorphin‐2 (Tyr‐Pro‐Phe‐Phe‐NH₂) binds with high affinity and selectivity to the μ‐opioid receptor. In the present study, [¹²⁵I]endomorphin‐2 has been used to characterize μ‐opioid‐binding sites on transplantable mouse mammary adenocarcinoma cells. Cold saturation experiments performed with [¹²⁵I]endomorphin‐2 (1 nm ) show biphasic binding curves in Scatchard coordinates. One component represents high affinity and low capacity (K_d = 18.79 ± 1.13 nm , B_max = 635 ± 24 fmol/mg protein) and the other shows low affinity and higher capacity (K_d = 7.67 ± 0.81 μm , B_max = 157 ± 13 pmol/mg protein) binding sites. The rank order of agonists competing for the [¹²⁵I]endomorphin‐2 binding site was [d ‐1‐Nal³]morphiceptin > endomorphin‐2 ? [d ‐Phe³]morphiceptin > morphiceptin > [d ‐1‐Nal³]endomorphin‐2, indicating binding of these peptides to μ‐opioid receptors. The uptake of ¹³¹I‐labeled peptides administered intraperitoneally to tumor‐bearing mice was also investigated. The highest accumulation in the tumor was observed for [d ‐1‐Nal³]morphiceptin, which reached the value of 8.19 ± 1.14% dose/g tissue.     

Syntheses and evaluation of 68Ga‐ and 153Sm‐labeled DOTA‐conjugated bisphosphonate ligand for potential use in detection of skeletal metastases and management of pain arising from skeletal metastases

This article reports the syntheses and evaluation of ⁶⁸Ga‐ and ¹⁵³Sm‐complexes of a new DOTA (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid)‐conjugated geminal bisphosphonate, DOTA‐Bn‐SCN‐BP, for their potential uses in the early detection of skeletal metastases by imaging and palliation of pain arising from skeletal metastases, respectively. The conjugate was synthesized in high purity following an easily adaptable three‐step reaction scheme. Gallium‐68‐ and ¹⁵³Sm‐complexes were prepared in high yield (>98%) and showed excellent in vitro stability in phosphate‐buffered saline (PBS) and human serum. Both the complexes showed high affinity for hydroxyapatite particles in in vitro binding study. In biodistribution studies carried out in normal Wistar rats, both the complexes exhibited rapid skeletal accumulation with almost no retention in any other major organ. The newly synthesized molecule DOTA‐Bn‐SCN‐BP would therefore be a promising targeting ligand for the development of radiopharmaceuticals for both imaging skeletal metastases and palliation of pain arising out of it in patients with cancer when radiolabeled with ⁶⁸Ga and ¹⁵³Sm, respectively. A systematic comparative evaluation, however, showed that there was no significant improvement of skeletal accumulation of the ¹⁵³Sm‐DOTA‐Bn‐SCN‐BP complex over ¹⁵³Sm‐DOTMP (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetramethylenephosphonic acid) as the later itself demonstrated optimal properties required for an agent for bone pain palliation.     

Design and synthesis of enantiopure 18F‐labelled [18F]trifluoromethyltryptophan from 2‐halotryptophan derivatives via copper(I)‐mediated [18F]trifluoromethylation and evaluation of its in vitro characterization for the serotonergic system imaging

We synthesized [¹⁸F]trifluoromethyl‐l ‐tryptophan ([¹⁸F]CF₃‐l ‐Trp) using Cu(I)‐mediated [¹⁸F]trifluoromethylation to image serotonergic system. Radiochemical yield was 6 ± 1.5% (n = 9), and radiochemical purity was over 99%. The molar activity was 0.44 to 0.76 GBq/μmol. [¹⁸F]CF₃‐l ‐Trp was stable for up to 6 hours in mouse and human sera at 37°C. Protein‐binding was 0.26 ± 0.03% and 0.34 ± 0.02% in human and mouse serum at 60 minutes, respectively. In conclusion, enantiopure [¹⁸F]CF₃‐l ‐Trp was synthesized as a feasible imaging agent for the serotonergic system.